# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        while l1 and l2:
            if l1.val+l2.val <= 10
            a = ListNode(l1.val+l2.val)
            l1 = l1.next
            l2 = l2.next
            a = a.next
            else:
                